Reliable retrieval is intrinsically rewarding: Recency, item difficulty, study session memory, and subjective confidence predict satisfaction in word-pair recall

The recall of a distant memory may appear satisfying and suggest successful retrieval is inherently rewarding. If the brain incentivizes retrieval attempts on the prospect of an internal retrieval reward, then the desire for that reward might natively reinforce declarative memory access. But what determines the level of retrieval satisfaction? We tested the idea that retrieval attempt uncertainty drives retrieval satisfaction. For instance, the more distant the memory, the more satisfying should it be to successfully retrieve it. Alternatively, the brain issues rewards based on the level of confidence in recall independent of the recall achievement. If so, then more confident retrieval is also more satisfying. In an online experiment containing five Swahili-English word pair study sessions spaced across one week, we tested 30 English-speaking participants’ recall satisfaction and memory confidence during learning as well as in a final cued recall test. We hypothesized that retrieval satisfaction should either increase or decrease with retrieval uncertainty as indicated by time since encoding, and how little in overall they recalled from the session. We found that retrieval satisfaction decreased with time since encoding and with study session retrieval performance. Moreover, we found that retrieval confidence and satisfaction ratings were highly related in the experiment. We also found a reliable interaction between confidence and word difficulty indicating that confidently recalled difficult items induced more satisfaction. Thus, the brain appears to reward both retrieval confidence and to a lesser extent, fruitful retrieval effort. Our findings may explain seemingly irrational self-regulated study behavior such as avoiding learning-efficient but difficult training protocols, as effects of a system rationally seeking to accrue intrinsic cognitive reward.

My understanding is as follows.Each point represents one participant.The participant in the green square represents someone who had a relatively good initial recall in the first session (e.g., mean correct recall in session 1 = .51)and a perfect recall in the least session (mean correct recall in session 5 = 1.0;I presumed this latter case applied to all cases, since the design followed a drop-out procedure).Thus, the retrieval improvement on the x-axis for the participant in green is 1.0 − .51= .49.The learning-related confidence change is the difference between the mean confidence for the correct attempts in session 1 and the mean confidence for the correct attempts in session 5.
Following the same logic, the retrieval improvement for the participant in the red box is the mean correct recall in session 5 (1.0) minus the mean correct recall in session 1 (e.g., 0.10).Thus, the retrieval improvement for the participant in the red box is high at .90.The corresponding difference in confidence ratings is low at 0.09.Is that reasoning correct?It would be helpful if the authors described in a short paragraph how they obtained one of the points in Fig. 1, panel A.

Minor points
In the following, I present a list of small suggestions to improve readability and compliance with Plos One copyediting standards.
-p.2, line 36-37: "We found that retrieval satisfaction decreased with time since encoding and study session retrieval performance".→ "We found that retrieval satisfaction decreased with time since encoding and with lower study session retrieval performance".
-p.5, line 105: "reward at play the presence of" → "reward at play in the presence".
-p.11, line 255: The data file in the OSF platform was uploaded with the .txtextension.
It would be more helpful if it were uploaded with the the .csvextension, as the OSF system would be able to read the file and print it on the screen of the web browser.
-p.12, line 289 (section "Encoding section results" and wherever applicable): The abbreviations for mean (M) and standard deviation (SD) should be reported in capital letters and italics.Please revise all such cases in the manuscript (e.g., p.15, section "Final recall test results").
-p.18, line 436: "z-scored JOL rating at study." → "z-scored JOL rating unit at study." -p.20, line 489: "…participants who did not complete the experiment were slightly more likely to be male …".Shouldn"t it be female?On p. 11, line 262, the authors say that "Of those who did not complete all sessions, 20 identified as female and 11 as male".So, the claim on p.20, line 489 should be "more likely to be female".
-p.20, line 499: "…, what then might the adaptive value … be?" → "…, what then might be the adaptive value …?" -p.22, line 542: Here I am not sure which preposition is the most appropriate, as it depends on the meaning the authors wish to convey.The text reads "It is also possible that the learning reward argument in curiosity theory is incorrect or at least that the hedonic "wanting" (Berridge & Kringlebcach, 2015) [Note: please use Plos One reference style here] aspect of reward is irrelevant in curiosity."Shouldn"t it be "irrelevant to curiosity"?
caption): The first letters should be capitalized in the boldface caption: "Study Session Learning and Ratings".In addition, the legends in the x-and yaxis should have the first letter of each word capitalized: x = Retrieval Improvement; y = Learning-related confidence change.Same applies for panels B and C. -p.13, line 317: References to Figures should be abbreviated (Figure 1 → Fig. 1; apply throughout the text for figure 1 → Fig. 1, figure 2 → Fig. 2, and figure 3 → Fig. 3).-p.15, line 362 (Figure 2 caption): The first letters are capitalized in the boldface caption: "Performance and Rating Associations".The legends in the x-and y-axis should have the first letter of each word capitalized: x = Estimated performance (Rasch); y = z(Satisfaction Rating).Same applies for panels B and C.